US20160026123A1 - Fixing device and image forming apparatus - Google Patents
Fixing device and image forming apparatus Download PDFInfo
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- US20160026123A1 US20160026123A1 US14/804,548 US201514804548A US2016026123A1 US 20160026123 A1 US20160026123 A1 US 20160026123A1 US 201514804548 A US201514804548 A US 201514804548A US 2016026123 A1 US2016026123 A1 US 2016026123A1
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Images
Classifications
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/20—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat
- G03G15/2003—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat using heat
- G03G15/2014—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat using heat using contact heat
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/20—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat
- G03G15/2003—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat using heat
- G03G15/2014—Apparatus for electrographic processes using a charge pattern for fixing, e.g. by using heat using heat using contact heat
- G03G15/2053—Structural details of heat elements, e.g. structure of roller or belt, eddy current, induction heating
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/80—Details relating to power supplies, circuits boards, electrical connections
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G2215/00—Apparatus for electrophotographic processes
- G03G2215/20—Details of the fixing device or porcess
- G03G2215/2003—Structural features of the fixing device
- G03G2215/2016—Heating belt
- G03G2215/2035—Heating belt the fixing nip having a stationary belt support member opposing a pressure member
Definitions
- the present invention relates to a fixing device which uses a heating method based on electromagnetic induction, and an image forming apparatus equipped with a fixing device which uses a heating method based on electromagnetic induction.
- a fixing device to be mounted in an image forming apparatus such as an electrophotographic printer and an electrophotographic printer is provided with a rotational heating member and a pressure roller which is kept pressed upon the heating member. It is configured to fix an unfixed toner image on a sheet of recording medium by heating the unfixed toner image and sheet while conveying the sheet through the nip which the heating member and pressure roller form between them.
- a fixing device which is provided with a magnetic circuit having an internal space through which an alternating magnetic flux passes, and a cylindrical member which is formed of an electrically conductive substance and which is disposed in the internal space of the magnetic circuit.
- the fixing device is configured so that the cylindrical member is heated by the electric current induced in the cylindrical member and the electrical resistance of the cylindrical member.
- the cylindrical member itself functions as a heater. Therefore, it has such a merit that it is simple in structure, and yet, high is thermal efficiency.
- the coil suddenly reduces in inductance. Consequently, a large amount of electric current flows through the coil, damaging thereby the electric power source.
- the core becomes saturated with magnetic flux as the amount by which magnetic flux is generated in the core reaches a specific value (point of saturation).
- FIG. 10 shows the relationship between the size of the cross section (at plane perpendicular to direction of magnetic flux) and magnetic flux saturation.
- the smaller the core in the size of its cross section the lower it is in the point of magnetic flux saturation.
- the occurrence of the saturation of the core with magnetic flux is related to core temperature; the higher the core temperature, the lower it is in the point of magnetic flux saturation.
- a fixing device for fixing an image on a recording material
- said fixing device comprising a rotatable member having an electroconductive layer; a helical coil provided inside rotatable member and having a helix axis extending in a generatrix direction of said rotatable member; a magnetic member provided in inside a helical configuration portion formed by said coil, said magnetic member does not form a loop outside said rotatable member; and a controller for controlling electric power supplied to said coil, wherein said electroconductive layer generates heat by electromagnetic induction caused by magnetic flux produced by an alternating current through said coil to fix the image on the recording material by the heat from said rotatable member, and wherein said controller limits maximum electric power supplied to said coil, in accordance with a temperature of said magnetic member.
- FIG. 1 is a schematic sectional view of a typical image forming apparatus to which the present invention is applicable, and shows the general structure of the apparatus.
- FIG. 2 is a schematic cross-sectional view of the essential portion of a typical fixing device to which the present invention is applicable.
- FIG. 3 is a schematic front view of the essential portion of the fixing device in FIG. 2 .
- FIG. 4 is a perspective view of the essential portion of the fixing device in FIG. 2 .
- FIG. 5 is a drawing which shows the relationship between the saturation magnetic flux and core temperature, in the first embodiment of the present invention.
- FIG. 6 is a drawing which shows the relationship between the amount of electric power consumption and the magnetic flux.
- FIG. 7 is a drawing which shows the relationship between the maximum allowable amount of electric power consumption and the core temperature.
- FIG. 8 is a drawing which shows the relationship among the measured sleeve temperature, measured core temperature, and print count.
- FIG. 9 is a drawing which shows the relationship among the measured sleeve temperature, measured core temperature, and length of elapsed time after the completion of a printing operation.
- FIG. 10 is a drawing which shows the relationship among the saturation magnetic flux, core temperature, and size of core cross-section.
- Parts (a) and (b) of FIG. 11 are schematic views illustrating the heat generation principle of the fixation sleeve.
- FIG. 1 is a schematic sectional view of an image forming apparatus 100 equipped with a fixing device, in the first embodiment. It shows the general structure of the apparatus.
- the image forming apparatus 100 is a laser beam printer which uses an electrophotographic image forming method.
- a referential code 101 stands for a photosensitive drum as an image bearing member. It is rotationally driven in the clockwise direction indicated by an arrow mark at a preset process speed (peripheral velocity). As the photosensitive drum 101 is rotationally driven, it is uniformly charged by a charge roller 102 to a preset polarity and a preset potential level.
- a referential code 103 stands for a laser beam scanner as an image exposing means.
- the scanner 103 scans (exposes) the charged peripheral surface of the photosensitive drum 101 with a beam L of laser light, which it outputs while modulating (turning on or off) the beam L with digital image formation signals which are inputted from an unshown external device such as a computer and are generated by an image processing means.
- an unshown external device such as a computer and are generated by an image processing means.
- a referential code 104 stands for a developing device, which has a development roller 104 a , from which the peripheral surface of the photosensitive drum 101 is supplied with developer (toner).
- developer toner
- the electrostatic latent image on the peripheral surface of the photosensitive drum 101 is continuously developed by the developer on the peripheral surface of the photosensitive drum 101 , starting from its downstream end in terms of the rotational direction of the photosensitive drum 101 .
- a referential code 105 stands for a sheet feeding cassette, in which multiple sheets of recording medium are stored in layers.
- a sheet feeding roller 106 is driven, whereby the sheets P in the sheet feeding cassette 105 are fed one by one by the sheet feeding roller 106 into the main assembly of the image forming apparatus 100 while being separated from the rest in the cassette 105 .
- each sheet P is sent to a pair of registration rollers 107 , and then, is sent by the registration rollers 107 to an area 108 T of transfer, which is the nip between the photosensitive drum 101 , and a transfer roller 108 which is rotated in contact with the photosensitive drum 101 by the rotation of the photosensitive drum 101 . That is, the conveyance of the sheet P is controlled by the pair of registration rollers 107 so that the leading edge of the image on the peripheral surface of the photosensitive drum 101 , and the leading edge of the sheet P arrive at the area 108 T of transfer at the same time.
- the sheet P is conveyed through the area 108 T of transfer while remaining pinched between the photosensitive drum 101 and transfer roller 108 .
- transfer voltage transfer bias
- the transfer bias applied to the transfer roller 108 is opposite in polarity from the toner.
- the toner image on the peripheral surface of the photosensitive drum 101 is electrostatically transferred onto the surface of the sheet P, in the area 108 T of transfer.
- the sheet P is separated from the peripheral surface of the photosensitive drum 101 , is conveyed through a sheet conveyance guide 109 , and is introduced into a fixing apparatus A (fixing device) as an image heating device.
- fixing apparatus A fixing device
- the sheet P is subjected by the fixing device A to a process for thermally fixing the toner image on the sheet P to the sheet P.
- the peripheral surface of the photosensitive drum 101 is cleared of transfer residual toner, paper dust, and the like contaminants by a cleaning device 110 , and then, is used for the formation of the next image.
- the sheet P is discharged onto a delivery tray 112 through a sheet outlet 111 .
- the fixing device A in this embodiment is a heating device which uses a heating method based on electromagnetic induction.
- FIG. 2 is a schematic cross-sectional view of the essential portion of the fixing device A.
- FIG. 3 is a schematic front view of the essential portion of the fixing device A.
- FIG. 4 is a perspective view of the essential portion of the fixing device A.
- a pressure roller 8 which is a pressure applying member (nip forming member) is made up of a metallic core 8 a , a heat resistant and elastic layer 8 b , and a release layer 8 c as a surface layer.
- the elastic layer 8 b is formed around the peripheral surface of the metallic core 8 a in the form of a roller which is coaxial with the metallic core and covers virtually the entirety of the peripheral surface of the metallic core 8 a .
- the material for the elastic layer 8 b such a substance as silicone rubber, fluorine rubber, fluoro-silicone rubber that is excellent in heat resistance is desired.
- the lengthwise ends of the metallic core 8 a are rotatably supported by the unshown pair of the lateral plates of the fixing device chassis, with the placement of a pair of electrically conductive bearings between the lengthwise ends and the pair of the lateral plates and, one for one.
- a pair of compression springs 17 a and 17 b are disposed in a compressed state between the lengthwise ends of a pressure application stay 5 , and a pair of spring bearing members 18 a and 18 b , respectively.
- the pressure application stay 5 remains pressured downward.
- the total amount of pressure to which the pressure application stay 5 is subjected is roughly 100 N-250 N (10 kgf-25 kgf).
- a fixation sleeve 1 which is a cylindrical and rotational member and has an electrically conductive layer, between the sleeve guiding member 6 and pressure roller 8 .
- a fixation nip N which has a preset width in terms of the recording medium conveyance direction is formed between the fixation sleeve 1 and pressure roller 8 .
- the pressure roller 8 is rotationally driven in the counterclockwise direction indicated by an arrow mark in the drawing by an unshown driving means.
- the fixation sleeve 1 is subjected to the rotational force attributable to the rotation of the pressure roller 8 and the friction between the fixation sleeve 1 and pressure roller 8 .
- the fixation sleeve 1 is rotated in the clockwise direction indicated by an arrow mark, with its inward surface sliding on the sleeve guiding member 6 by its inward surface.
- a sheet P of recording medium is introduced into the fixation nip N, and is conveyed through the fixation nip N while remaining pinched between the fixation sleeve 1 and pressure roller 8 .
- a pair of flanging members 12 a and 12 b are fitted around the left and right end portions of the sleeve guide 6 , in such a manner that they are allowed to rotate around the sleeve guide 6 . In terms of their movement in the left-right direction, they are prevented from moving by a pair of regulating members 13 a and 13 b . They play the role of regulating the movement of the fixation sleeve 1 in the direction parallel to the lengthwise direction of the sleeve guide 6 , by catching the fixation sleeve 1 by the lengthwise ends of the fixation sleeve 1 when the fixation sleeve 1 rotates.
- LCP Liquid Crystal Polymer
- the front side is the side from which a sheet P of recording medium is introduced into the fixing device A.
- the left or right side is the left or right side as the fixing device A is seen from the front side.
- the fixation sleeve 1 is a cylindrical and rotatable heating member which has a multilayer structure. More concretely, it has: a heat generation layer 1 a (electrically conductive layer), as a substrative layer, which is formed of an electrically conductive substance; an elastic layer 1 b layered upon the peripheral surface of the heat generation layer 1 a ; and a release layer 1 c layered on the outward surface of the elastic layer 1 b .
- the smaller the fixation sleeve 1 in diameter the smaller a heating device can be structured in overall size, and also, the smaller the fixation sleeve 1 in thermal capacity.
- the fixation sleeve 1 in diameter the faster it is in the speed at which it increases in temperature as it is heated.
- austenitic stainless steels copper, aluminum, or sliver, which is small in permeability, is used.
- the fixation sleeve 1 is made excessively small in diameter, it is possible that it will come into contact with such components as an excitation coil 3 which is disposed in the hollow of the fixation sleeve 1 , being thereby prevented from smoothly rotating and/or being robbed of heat.
- excessively reducing the fixation sleeve 1 in diameter will possibly affect sheet conveyance and/or performance of the fixing device A.
- the fixation sleeve 1 a magnetic core which was reduced in diameter with the use of the method (which is described later), was employed as the fixation sleeve 1 .
- the heat generation layer 1 a is a piece of metallic film which is 10-50 ⁇ m in thickness.
- the elastic layer 1 b is formed of silicone rubber which is 20 degrees in hardness (JIS-A, application of 1 kg of weight). It is 0.1 mm-0.3 mm in thickness.
- the elastic layer 1 b is covered with the surface layer 1 c (release layer), which is a piece of tube made of fluorine resin and is 10 ⁇ m-50 ⁇ m in thickness.
- the heat generation layer 1 a is subjected to alternating magnetic flux to induce electric current in the heat generation layer 1 a , so that heat is generated in the heat generation layer 1 a .
- the thus generated heat is conducted to the elastic layer 1 b and release layer 1 c , heating thereby the entirety of the fixation sleeve 1 , and heats a sheet P of recording medium and a toner image T on the sheet P as the sheet P is conveyed through the fixation nip N. Consequently, the toner image T is fixed to the sheet P.
- FIG. 4 is a perspective view of the essential portion of the fixing device A. It shows the structure of the fixing device A.
- the magnetic core 2 which is a magnetic core member is disposed with the use of an unshown fixing means in such a manner that it is put through the hollow of the fixation sleeve 1 .
- a linear and open magnetic circuit which has magnetic poles NP and SP is formed. More concretely, the magnetic core 2 , the lengthwise direction of which coincides with the direction of the generatrix of the fixation sleeve 1 , is put through the hollow of the fixation sleeve 1 .
- the magnetic core 2 is in such a shape that does not form a loop outside the fixation sleeve 1 . That is, the magnetic core 2 is in such a shape that has two ends. Thus, it forms an open magnetic circuit, that is, a magnetic circuit, a part of which is missing.
- a ferromagnetic substance which is small in hysteresis loss and high in specific permeability is desirable. That is, a ferromagnetic member which is formed of sintered ferrite, ferrite resin, amorphous metallic alloy, or oxide or metallic alloy, such as Permalloy, which is high in permeability, is desirable as the magnetic core 2 .
- the excitation coil 3 which is placed in the hollow of the fixation sleeve 1 is formed by spirally winding ordinary electrically conductive wire around the magnetic core 2 . That is, the excitation coil 3 is wound around the peripheral surface of the magnetic core 2 , directly or with the placement of a bobbin or the like between the excitation coil 3 and magnetic core 2 , in the direction perpendicular to the above-mentioned generatrix of the magnetic core 2 .
- the fixing device A in this embodiment is configured so that as magnetic flux comes out of one end of the magnetic core 2 , it returns to the other end of the magnetic core 2 by no less than 70%, preferably, 90%, through the outward adjacencies of the electrically conductive layer 1 a . That is, the fixing device A is structured so that the combination of the electrically conductive layer 1 a and coil 3 becomes high in coupling coefficient.
- part (b) of FIG. 11 the fixing device A in this embodiment is configured so that as magnetic flux comes out of one end of the magnetic core 2 , it returns to the other end of the magnetic core 2 by no less than 70%, preferably, 90%, through the outward adjacencies of the electrically conductive layer 1 a . That is, the fixing device A is structured so that the combination of the electrically conductive layer 1 a and coil 3 becomes high in coupling coefficient.
- the electrically conductive layer 1 a is heated by the Joule's heat generated by an electric current J which flows through the electrically conductive layer 1 a in the direction perpendicular to the circumference of the fixation sleeve 1 .
- the electrically conductive layer 1 a is made to generate heat by the electrical current J which is generated by the magnetic flux, the direction of which is parallel to the generatrix of the fixation sleeve 1 . That is, the electrically conductive layer 1 a is made to generate heat, primarily by the electric current J which flows in the direction which is parallel to the circumferential direction of the electrically conductive layer 1 a.
- a referential code 40 stands for a control circuit (controlling section).
- Each of temperature detection elements 9 , 10 , and 11 is a thermistor of the so-called non-contact type. It detects the temperature of the fixation sleeve 1 (section for obtaining fixation sleeve temperature).
- the signals (electrical signals related to detected temperature) from the temperature detection elements 9 , 10 and 11 are compared with the signal values which correspond to preset target temperature levels, by the engine controlling section (setting section) 43 of the control circuit 40 .
- the engine controlling section 43 of the control circuit 40 decides the amount by which electric power is to be inputted into the high frequency converter 16 .
- the electric power controlling section 46 of the control circuit 40 supplies the high frequency converter 16 with electric power by the decided amount.
- the magnetic core 2 is in contact with a temperature detection element 14 which is a temperature obtaining section for detecting (obtaining) the temperature of the magnetic core 2 .
- the information about the temperature detected by the temperature detection element 14 is inputted into the engine control section 43 , which sets the maximum amount for the magnetic flux, according to the results (obtained temperature levels). Setting of the maximum amount for the magnetic flux is described later in detail.
- FIG. 5 is a drawing which shows the relationship between the amount of the magnetic flux in the magnetic core 2 , and the temperature of the magnetic core 2 , when the magnetic core 2 is saturated with the magnetic flux.
- the temperature of the magnetic core 2 becomes highest when the image forming apparatus is continuously used for a substantial length of time to continuously output a substantial number of prints. More specifically, it reached the highest level as the image forming apparatus was operated to continuously output a substantial number of prints for roughly 60 minutes.
- the high level of the temperature was in a range of 190° C.-200° C.
- the maximum amount is set for the magnetic flux which the excitation coil 3 is made to generate, according to the temperature of the magnetic core 2 .
- the maximum amount for the magnetic flux is set by converting the magnetic flux density into an equivalent amount of electric power, and then, the largest amount by which the excitation coil 3 is supplied with electric power is set to the value of this equivalent amount of electric power. Setting the maximum amount by which the excitation coil 3 is supplied with electric power is to control (limit) the maximum amount by which the excitation coil 3 is allowed to be supplied with electric power.
- FIG. 7 In which a solid line represents the relationship between the core temperature and the maximum amount by which the excitation coil 3 can be supplied with electric power without saturating the excitation coil 3 with magnetic flux.
- the maximum amount of electric power is set according to the magnetic core temperature as shown by a broken line in FIG. 7 .
- the largest amount by which the excitation coil 3 is allowed to be supplied with electric power was set as shown in Table 1. Then, the length of time it took for the temperature of the fixation sleeve 1 to reach the level (target level) at which the fixing device A became ready for image fixation after electric power began to be supplied to the excitation coil 3 when the magnetic core temperature was 25° C., 100° C., 150° C. and 180° C., was measured.
- the maximum amount of electric power was set to 450 W regardless of the temperature of the magnetic core 2 . Also in the case of this setting, the length of time it took for the fixation sleeve 1 to reach the fixation-possible-temperature was measured.
- Second example of comparative control in order to prevent the magnetic core 2 from being saturated with the magnetic flux, even if the excitation coil 3 is supplied with 1500 W of electric power when the magnetic core temperature was 200° C., the magnetic core 2 was made to 250 mm 2 in the size of its cross-section. Accordingly, the fixation sleeve 1 was increased in internal diameter to 40 mm. Also in the case of the comparative control, the length of time it took for the temperature of the fixation sleeve 1 to reach the fixation-possible-level was measured.
- the target length of time for the temperature of the fixation sleeve 1 to reach the fixation-possible-level was set to be no more than 7.5 seconds.
- the maximum amount for the electric power is limited to small value. That is, the engine controlling section 43 (setting section) sets the maximum amount of electric power in such a manner that the higher the magnetic core temperature (obtained temperature) is, the smaller the maximum amount of electric power.
- the fixing device itself may have warmed up, it does not require a large amount of heat to make the fixation sleeve 1 reach the fixation-possible-temperature. Therefore, even if the maximum amount of electric power is small, it is possible to make the fixation sleeve 1 reach the fixation-possible-temperature in a short length of time.
- the maximum amount of electric power may be set to be larger. Therefore, even if the heating device itself has not warmed up, it is possible to make the fixation sleeve 1 reach the fixation-possible-temperature within a short length of time.
- the amount by which the excitation coil 3 was supplied with electric power was kept at 1500 W regardless of the magnetic core temperature.
- the fixation sleeve 1 was increased in internal diameter, it was greater in thermal capacity. Therefore, in a case where the magnetic core temperature was high, it was possible to make the fixation sleeve 1 reach the fixation-possible-temperature within the target length of time. On the other hand, in a case where the magnetic core temperature was low, it was impossible to make the fixation sleeve 1 reach the fixation-possible-temperature.
- the fixing device A with a means for detecting the temperature of its magnetic core 2 , and adjusting the maximum amount by which magnetic flux is allowed to be generated by the excitation coil 3 , according to the magnetic core temperature, it was possible to make the fixation sleeve 1 to reach the fixation-possible-temperature within a short length of time, even when the magnetic core 2 was reduced in size.
- the method for limiting the maximum amount by which the excitation coil 3 is supplied with electric power does not need to be limited to the one in this embodiment, which changes the amount in steps according to the magnetic core temperature.
- a method that changes the maximum amount in a step-less manner according to the magnetic core temperature may be employed.
- the temperature obtaining section for obtaining the temperature of the magnetic core 2 was the temperature detection element 14 , with which the magnetic core 2 was provided.
- the temperature obtaining section for obtaining the temperature of the magnetic core 2 does not need to be limited to the temperature detection element 14 .
- it may be such a means (temperature estimating means) that is for estimating (predicting) the magnetic core temperature.
- such a means was employed as the temperature obtaining section.
- the magnetic core temperature is estimated based on the temperature detection history of the temperature detection elements 9 , 10 and 11 , and the printing operation history of the image forming apparatus 100 .
- the temperature obtaining section which obtains the temperature of the magnetic core 2 comprises: the temperature detection elements 9 , 10 and 11 , which detect the temperature of the fixation sleeve 1 ; and a temperature estimating section 43 (engine controlling section) which estimates the temperature of the magnetic core 2 based on the temperature detected by these temperature detection elements 9 , 10 and 11 .
- FIG. 8 shows the relationship among the measured temperature of the fixation sleeve 1 , measured temperature of the magnetic core 2 , and print count, when a substantial number of prints were continuously outputted.
- the magnetic core temperature increased. More specifically, as the print count reached roughly 2,500, the magnetic core temperature reached 190° C. In particular, during the initial period of operation which was high in the rate of temperature increase, the magnetic core temperature increased roughly 90° C. while 500 prints were outputted. In other words, the rate of temperature increase was 0.18° C./print. Further, there seems to be virtually no correlation between the fixation sleeve temperature and magnetic core temperature.
- the engine controlling section 43 estimates temperature T 0 , at which the magnetic core temperature will be at the starting of a printing operation, and temperature T 1 , at which the magnetic core temperature will be during the printing operation, as follows.
- T 1 T 0+0.18 ⁇ n (however, if T 1 >190° C., T 1 is assumed to be 190° C.)
- T 0 T 2 ⁇ ( T 2 ⁇ Ts ) ⁇ t/ 3000.
- T 2 length of time having elapsed since the completion of the preceding job
- Table 3 shows the settings for the maximum amount of electric power.
- the temperature of the magnetic core was estimated, unlike in the first embodiment. Therefore, the maximum amount of electric power was set to values which were slightly smaller than those in the first embodiment. Then, the length of time it took for the fixation sleeve 1 to reach the fixation-possible-temperature after the magnetic core 2 began to be supplied with electric power was measured when the estimated temperature of the magnetic core 2 was 25° C., 100° C., 150° C. and 180° C.
- the maximum amount of electric power was set to 450 W regardless of the temperature of the magnetic core 2 . Then, the length of time it took for the fixation sleeve 1 to reach its fixation-possible-temperature was measured as it was in the tests in which the control in the first embodiment was verified.
- the magnetic core 2 in order to prevent the magnetic core 2 from becoming saturated with magnetic flux even if the excitation coil 3 is supplied with 1,500 W of electric power when the magnetic core temperature is 200° C., the magnetic core 2 was made to be 250 mm 2 in the size of its cross-section. Thus, the fixation sleeve 1 was increased in internal diameter to 40 mm. Then, the length of time it took for the fixation sleeve 1 to reach its fixation-possible-temperature was measured.
- the length of time it took for the fixation sleeve 1 to reach the fixation-possible-temperature was no more than 7.5 seconds, which is the target length of time.
- the fixation sleeve 1 did not reach the fixation-possible-temperature within the target length of time.
- the fixing device A was provided with a temperature estimating section for estimating the magnetic core temperature, and the maximum amount by which magnetic flux allowed to be generated by the excitation coil 3 was changed according to the estimated temperature of the magnetic core 2 .
- the fixation sleeve 1 reach its fixation-possible-temperature within a short length of time.
- the temperature of the magnetic core 2 was estimated by mathematical calculation based on the temperature of the fixation sleeve 1 and the history of the preceding printing operation. However, it may be based on only the history of the preceding printing operation, or the temperature of the fixation sleeve 1 , that the temperature of the magnetic core 2 is estimated. That is, the fixing device A was configured so that its temperature obtaining section was the temperature estimating section 43 (engine controlling section) which estimates the temperature of the magnetic core 2 based on the history of the printing operation carried out by the image forming apparatus 100 .
- the fixing device A is configured so that the temperature obtaining section is made up of a combination of a temperature detection element 15 ( FIG. 4 ) which detects the ambient temperature of the internal space of the image forming apparatus 100 , and the temperature estimating section 43 (engine controlling section) which estimates the temperature of the magnetic core based on the temperature detected by the temperature detection element 15 .
- a fixing device includes not only a heating device for fixing an unfixed toner image on a sheet of recording medium to the sheet, but also, a heating device for applying heat and pressure to the temporarily or permanently fixed image on a sheet of recording medium for the second time to improve the image in glossiness.
- the cylindrical and rotational heating member having the electrically conductive layer 1 a was the flexible fixation sleeve 1 .
- the cylindrical, flexible, and rotational heating member having the electrically conductive layer 1 a may be a flexible endless belt which is suspended, and kept tensioned, by two or more belt suspending members, and which is rotationally (circularly) driven.
- it may be a hard and hollow roller, for example, a piece of hollow pipe.
- the fixing device A was configured so that the electrically conductive layer 1 a is made to generate heat (Joule's heat) by the electric current which flows through the electrically conductive layer 1 a in the direction parallel to the circumferential direction of the layer 1 a .
- the present invention is also applicable to a fixing device which is configured so that the electrically conductive layer 1 a is made to generate heat (Joule's heat) by the eddy current induced in the electrically conductive layer 1 a.
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Abstract
Description
- The present invention relates to a fixing device which uses a heating method based on electromagnetic induction, and an image forming apparatus equipped with a fixing device which uses a heating method based on electromagnetic induction.
- Generally speaking, a fixing device to be mounted in an image forming apparatus such as an electrophotographic printer and an electrophotographic printer is provided with a rotational heating member and a pressure roller which is kept pressed upon the heating member. It is configured to fix an unfixed toner image on a sheet of recording medium by heating the unfixed toner image and sheet while conveying the sheet through the nip which the heating member and pressure roller form between them.
- In recent years, there has been proposed a fixing device which uses a heating method based on electromagnetic induction. This type of fixing device is capable of generating heat directly in its rotational heating member, being therefor shorter in warm-up time than the other types of fixing device. It has also such a merit that it is less in electric power consumption than the other types of fixing device.
- There is disclosed in Japanese Laid-open Patent Application S51-120451, a fixing device which is provided with a magnetic circuit having an internal space through which an alternating magnetic flux passes, and a cylindrical member which is formed of an electrically conductive substance and which is disposed in the internal space of the magnetic circuit. The fixing device is configured so that the cylindrical member is heated by the electric current induced in the cylindrical member and the electrical resistance of the cylindrical member. In the case of this fixing device, the cylindrical member itself functions as a heater. Therefore, it has such a merit that it is simple in structure, and yet, high is thermal efficiency.
- Also in recent years, it has been desired to reduce the aforementioned rotational heating member in diameter, in order to reduce a fixing device in size and to reduce the rotational heating member in thermal capacity. One of the methods for achieving such an objective is to reduce in size the coil and core which are disposed in the internal space of the rotational heating member. However, reducing the core in size makes it necessary to take into consideration, the phenomenon that the core becomes saturated with magnetic flux.
- As the core is saturated with magnetic flux, the coil suddenly reduces in inductance. Consequently, a large amount of electric current flows through the coil, damaging thereby the electric power source. The core becomes saturated with magnetic flux as the amount by which magnetic flux is generated in the core reaches a specific value (point of saturation).
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FIG. 10 shows the relationship between the size of the cross section (at plane perpendicular to direction of magnetic flux) and magnetic flux saturation. As is evident fromFIG. 10 , the smaller the core in the size of its cross section, the lower it is in the point of magnetic flux saturation. Further, the occurrence of the saturation of the core with magnetic flux is related to core temperature; the higher the core temperature, the lower it is in the point of magnetic flux saturation. - In the past, therefore, in order to prevent the problem that magnetic flux is generated by an amount which is greater than the amount which is large enough to saturate the core with magnetic flux, it was necessary to limit (control) the amount by which magnetic flux is generated in the core. However, reducing the core in size to reduce the rotational heating member in size limits the amount by which magnetic flux is allowed to be generated. Thus, reducing the rotational heating member in size to reduce the rotational heating member in thermal capacity is not satisfactorily, because it increases the heating device in the length of startup time. In other words, it increases the fixing device in the length of FPOP (First Print Out Time).
- According to an aspect of the present invention, there is provided a fixing device for fixing an image on a recording material, said fixing device comprising a rotatable member having an electroconductive layer; a helical coil provided inside rotatable member and having a helix axis extending in a generatrix direction of said rotatable member; a magnetic member provided in inside a helical configuration portion formed by said coil, said magnetic member does not form a loop outside said rotatable member; and a controller for controlling electric power supplied to said coil, wherein said electroconductive layer generates heat by electromagnetic induction caused by magnetic flux produced by an alternating current through said coil to fix the image on the recording material by the heat from said rotatable member, and wherein said controller limits maximum electric power supplied to said coil, in accordance with a temperature of said magnetic member.
- Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
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FIG. 1 is a schematic sectional view of a typical image forming apparatus to which the present invention is applicable, and shows the general structure of the apparatus. -
FIG. 2 is a schematic cross-sectional view of the essential portion of a typical fixing device to which the present invention is applicable. -
FIG. 3 is a schematic front view of the essential portion of the fixing device inFIG. 2 . -
FIG. 4 is a perspective view of the essential portion of the fixing device inFIG. 2 . -
FIG. 5 is a drawing which shows the relationship between the saturation magnetic flux and core temperature, in the first embodiment of the present invention. -
FIG. 6 is a drawing which shows the relationship between the amount of electric power consumption and the magnetic flux. -
FIG. 7 is a drawing which shows the relationship between the maximum allowable amount of electric power consumption and the core temperature. -
FIG. 8 is a drawing which shows the relationship among the measured sleeve temperature, measured core temperature, and print count. -
FIG. 9 is a drawing which shows the relationship among the measured sleeve temperature, measured core temperature, and length of elapsed time after the completion of a printing operation. -
FIG. 10 is a drawing which shows the relationship among the saturation magnetic flux, core temperature, and size of core cross-section. - Parts (a) and (b) of
FIG. 11 are schematic views illustrating the heat generation principle of the fixation sleeve. -
FIG. 1 is a schematic sectional view of animage forming apparatus 100 equipped with a fixing device, in the first embodiment. It shows the general structure of the apparatus. Theimage forming apparatus 100 is a laser beam printer which uses an electrophotographic image forming method. Areferential code 101 stands for a photosensitive drum as an image bearing member. It is rotationally driven in the clockwise direction indicated by an arrow mark at a preset process speed (peripheral velocity). As thephotosensitive drum 101 is rotationally driven, it is uniformly charged by acharge roller 102 to a preset polarity and a preset potential level. - A
referential code 103 stands for a laser beam scanner as an image exposing means. Thescanner 103 scans (exposes) the charged peripheral surface of thephotosensitive drum 101 with a beam L of laser light, which it outputs while modulating (turning on or off) the beam L with digital image formation signals which are inputted from an unshown external device such as a computer and are generated by an image processing means. Thus, the exposed points of the charged peripheral surface of thephotosensitive drum 101 are discharged. Consequently, an electrostatic latent image, which reflects the image formation signals, is effected on the peripheral surface of thephotosensitive drum 101. - A
referential code 104 stands for a developing device, which has adevelopment roller 104 a, from which the peripheral surface of thephotosensitive drum 101 is supplied with developer (toner). The electrostatic latent image on the peripheral surface of thephotosensitive drum 101 is continuously developed by the developer on the peripheral surface of thephotosensitive drum 101, starting from its downstream end in terms of the rotational direction of thephotosensitive drum 101. - A
referential code 105 stands for a sheet feeding cassette, in which multiple sheets of recording medium are stored in layers. As theimage forming apparatus 100 receives a signal for starting recording medium conveyance, asheet feeding roller 106 is driven, whereby the sheets P in thesheet feeding cassette 105 are fed one by one by thesheet feeding roller 106 into the main assembly of theimage forming apparatus 100 while being separated from the rest in thecassette 105. Then, each sheet P is sent to a pair ofregistration rollers 107, and then, is sent by theregistration rollers 107 to anarea 108T of transfer, which is the nip between thephotosensitive drum 101, and atransfer roller 108 which is rotated in contact with thephotosensitive drum 101 by the rotation of thephotosensitive drum 101. That is, the conveyance of the sheet P is controlled by the pair ofregistration rollers 107 so that the leading edge of the image on the peripheral surface of thephotosensitive drum 101, and the leading edge of the sheet P arrive at thearea 108T of transfer at the same time. - Thereafter, the sheet P is conveyed through the
area 108T of transfer while remaining pinched between thephotosensitive drum 101 andtransfer roller 108. While the sheet P is conveyed through thearea 108T of transfer, transfer voltage (transfer bias), which is kept stable in amplitude at a preset value is applied to thetransfer roller 108 from an unshown transfer bias application power source. More specifically, the transfer bias applied to thetransfer roller 108 is opposite in polarity from the toner. Thus, the toner image on the peripheral surface of thephotosensitive drum 101 is electrostatically transferred onto the surface of the sheet P, in thearea 108T of transfer. After the transfer, the sheet P is separated from the peripheral surface of thephotosensitive drum 101, is conveyed through asheet conveyance guide 109, and is introduced into a fixing apparatus A (fixing device) as an image heating device. - The sheet P is subjected by the fixing device A to a process for thermally fixing the toner image on the sheet P to the sheet P. After the transfer of the toner image from the peripheral surface of the
photosensitive drum 101 to the sheet P, the peripheral surface of thephotosensitive drum 101 is cleared of transfer residual toner, paper dust, and the like contaminants by acleaning device 110, and then, is used for the formation of the next image. After being conveyed through the fixing device A, the sheet P is discharged onto adelivery tray 112 through asheet outlet 111. - The fixing device A in this embodiment is a heating device which uses a heating method based on electromagnetic induction.
FIG. 2 is a schematic cross-sectional view of the essential portion of the fixing device A.FIG. 3 is a schematic front view of the essential portion of the fixing device A.FIG. 4 is a perspective view of the essential portion of the fixing device A. - A
pressure roller 8 which is a pressure applying member (nip forming member) is made up of ametallic core 8 a, a heat resistant andelastic layer 8 b, and arelease layer 8 c as a surface layer. Theelastic layer 8 b is formed around the peripheral surface of themetallic core 8 a in the form of a roller which is coaxial with the metallic core and covers virtually the entirety of the peripheral surface of themetallic core 8 a. As the material for theelastic layer 8 b, such a substance as silicone rubber, fluorine rubber, fluoro-silicone rubber that is excellent in heat resistance is desired. The lengthwise ends of themetallic core 8 a are rotatably supported by the unshown pair of the lateral plates of the fixing device chassis, with the placement of a pair of electrically conductive bearings between the lengthwise ends and the pair of the lateral plates and, one for one. - Referring to
FIG. 3 , a pair of compression springs 17 a and 17 b are disposed in a compressed state between the lengthwise ends of apressure application stay 5, and a pair ofspring bearing members pressure application stay 5 remains pressured downward. By the way, in the case of the fixing device A in this embodiment, the total amount of pressure to which thepressure application stay 5 is subjected is roughly 100 N-250 N (10 kgf-25 kgf). - Thus, the bottom surface of a
sleeve guiding member 6, which is formed of heat resistant resin such as PPS, and the upwardly facing portion of the peripheral surface of thepressure roller 8 are pressed against each other, with the presence of afixation sleeve 1 which is a cylindrical and rotational member and has an electrically conductive layer, between thesleeve guiding member 6 andpressure roller 8. Thus, a fixation nip N which has a preset width in terms of the recording medium conveyance direction is formed between thefixation sleeve 1 andpressure roller 8. - The
pressure roller 8 is rotationally driven in the counterclockwise direction indicated by an arrow mark in the drawing by an unshown driving means. Thus, thefixation sleeve 1 is subjected to the rotational force attributable to the rotation of thepressure roller 8 and the friction between thefixation sleeve 1 andpressure roller 8. Thus, thefixation sleeve 1 is rotated in the clockwise direction indicated by an arrow mark, with its inward surface sliding on thesleeve guiding member 6 by its inward surface. A sheet P of recording medium is introduced into the fixation nip N, and is conveyed through the fixation nip N while remaining pinched between thefixation sleeve 1 andpressure roller 8. - A pair of
flanging members sleeve guide 6, in such a manner that they are allowed to rotate around thesleeve guide 6. In terms of their movement in the left-right direction, they are prevented from moving by a pair of regulatingmembers fixation sleeve 1 in the direction parallel to the lengthwise direction of thesleeve guide 6, by catching thefixation sleeve 1 by the lengthwise ends of thefixation sleeve 1 when thefixation sleeve 1 rotates. As the maternal for theflanging members - Regarding the positioning of the fixing device A, the front side is the side from which a sheet P of recording medium is introduced into the fixing device A. The left or right side is the left or right side as the fixing device A is seen from the front side.
- The
fixation sleeve 1 is a cylindrical and rotatable heating member which has a multilayer structure. More concretely, it has: aheat generation layer 1 a (electrically conductive layer), as a substrative layer, which is formed of an electrically conductive substance; anelastic layer 1 b layered upon the peripheral surface of theheat generation layer 1 a; and a release layer 1 c layered on the outward surface of theelastic layer 1 b. The smaller thefixation sleeve 1 in diameter, the smaller a heating device can be structured in overall size, and also, the smaller thefixation sleeve 1 in thermal capacity. Thus, the smaller thefixation sleeve 1 in diameter, the faster it is in the speed at which it increases in temperature as it is heated. As the material for the electricallyconductive layer 1 a, austenitic stainless steels, copper, aluminum, or sliver, which is small in permeability, is used. - However, if the
fixation sleeve 1 is made excessively small in diameter, it is possible that it will come into contact with such components as anexcitation coil 3 which is disposed in the hollow of thefixation sleeve 1, being thereby prevented from smoothly rotating and/or being robbed of heat. Thus, excessively reducing thefixation sleeve 1 in diameter will possibly affect sheet conveyance and/or performance of the fixing device A. - In this embodiment, a magnetic core which was reduced in diameter with the use of the method (which is described later), was employed as the
fixation sleeve 1. Thus, it was possible to employ a sleeve which was as small as 30 mm in diameter. Theheat generation layer 1 a is a piece of metallic film which is 10-50 μm in thickness. Theelastic layer 1 b is formed of silicone rubber which is 20 degrees in hardness (JIS-A, application of 1 kg of weight). It is 0.1 mm-0.3 mm in thickness. Theelastic layer 1 b is covered with the surface layer 1 c (release layer), which is a piece of tube made of fluorine resin and is 10 μm-50 μm in thickness. - The
heat generation layer 1 a is subjected to alternating magnetic flux to induce electric current in theheat generation layer 1 a, so that heat is generated in theheat generation layer 1 a. The thus generated heat is conducted to theelastic layer 1 b and release layer 1 c, heating thereby the entirety of thefixation sleeve 1, and heats a sheet P of recording medium and a toner image T on the sheet P as the sheet P is conveyed through the fixation nip N. Consequently, the toner image T is fixed to the sheet P. - Next, the system which induces electric current in the
heat generation layer 1 a by subjecting theheat generation layer 1 a to alternating magnetic flux is described in detail.FIG. 4 is a perspective view of the essential portion of the fixing device A. It shows the structure of the fixing device A. Themagnetic core 2 which is a magnetic core member is disposed with the use of an unshown fixing means in such a manner that it is put through the hollow of thefixation sleeve 1. Thus, a linear and open magnetic circuit which has magnetic poles NP and SP is formed. More concretely, themagnetic core 2, the lengthwise direction of which coincides with the direction of the generatrix of thefixation sleeve 1, is put through the hollow of thefixation sleeve 1. Themagnetic core 2 is in such a shape that does not form a loop outside thefixation sleeve 1. That is, themagnetic core 2 is in such a shape that has two ends. Thus, it forms an open magnetic circuit, that is, a magnetic circuit, a part of which is missing. - As the material for the
magnetic core 2, a ferromagnetic substance which is small in hysteresis loss and high in specific permeability is desirable. That is, a ferromagnetic member which is formed of sintered ferrite, ferrite resin, amorphous metallic alloy, or oxide or metallic alloy, such as Permalloy, which is high in permeability, is desirable as themagnetic core 2. - In this embodiment, a magnetic core made, by sintering, of ferrite which is 1800 in specific permeability, is used as the
magnetic core 2. It is cylindrical, and is 240 mm in length. In this embodiment, it was possible to employ a magnetic member which is as small as 120 mm2 in cross-sectional size at a plane perpendicular to the direction X inFIG. 4 (direction parallel to rotational axis, or generatrix, of fixation sleeve 1) as themagnetic core 2. - The
excitation coil 3 which is placed in the hollow of thefixation sleeve 1 is formed by spirally winding ordinary electrically conductive wire around themagnetic core 2. That is, theexcitation coil 3 is wound around the peripheral surface of themagnetic core 2, directly or with the placement of a bobbin or the like between theexcitation coil 3 andmagnetic core 2, in the direction perpendicular to the above-mentioned generatrix of themagnetic core 2. Therefore, as high frequency electric current (alternating electric current) is flowed through theexcitation coil 3 by way of a pair ofpower supply contacts high frequency converter 16, or the like, magnetic flux which is parallel to the direction of the generatrix of thefixation sleeve 1 is generated. - Next, the principle based on which heat is generated in the
fixation sleeve 1 of the fixing device A is described. Referring to part (a) of FIG. 11, the fixing device A in this embodiment is configured so that as magnetic flux comes out of one end of themagnetic core 2, it returns to the other end of themagnetic core 2 by no less than 70%, preferably, 90%, through the outward adjacencies of the electricallyconductive layer 1 a. That is, the fixing device A is structured so that the combination of the electricallyconductive layer 1 a andcoil 3 becomes high in coupling coefficient. Next, referring to part (b) ofFIG. 11 , the electricallyconductive layer 1 a is heated by the Joule's heat generated by an electric current J which flows through the electricallyconductive layer 1 a in the direction perpendicular to the circumference of thefixation sleeve 1. In other words, the electricallyconductive layer 1 a is made to generate heat by the electrical current J which is generated by the magnetic flux, the direction of which is parallel to the generatrix of thefixation sleeve 1. That is, the electricallyconductive layer 1 a is made to generate heat, primarily by the electric current J which flows in the direction which is parallel to the circumferential direction of the electricallyconductive layer 1 a. - Next, referring to
FIG. 4 , the method (electric power controlling method) for controlling the fixing device A in temperature is described. Areferential code 40 stands for a control circuit (controlling section). Each oftemperature detection elements temperature detection elements control circuit 40. Based on the results of the comparison, theengine controlling section 43 of thecontrol circuit 40 decides the amount by which electric power is to be inputted into thehigh frequency converter 16. The electricpower controlling section 46 of thecontrol circuit 40 supplies thehigh frequency converter 16 with electric power by the decided amount. - Further, the
magnetic core 2 is in contact with atemperature detection element 14 which is a temperature obtaining section for detecting (obtaining) the temperature of themagnetic core 2. The information about the temperature detected by thetemperature detection element 14 is inputted into theengine control section 43, which sets the maximum amount for the magnetic flux, according to the results (obtained temperature levels). Setting of the maximum amount for the magnetic flux is described later in detail. -
FIG. 5 is a drawing which shows the relationship between the amount of the magnetic flux in themagnetic core 2, and the temperature of themagnetic core 2, when themagnetic core 2 is saturated with the magnetic flux. The higher themagnetic core 2 in temperature, the smaller themagnetic core 2 in the amount of saturation magnetic flux. Moreover, in the case of the image forming apparatus in this embodiment, the temperature of themagnetic core 2 becomes highest when the image forming apparatus is continuously used for a substantial length of time to continuously output a substantial number of prints. More specifically, it reached the highest level as the image forming apparatus was operated to continuously output a substantial number of prints for roughly 60 minutes. The high level of the temperature was in a range of 190° C.-200° C. - In this embodiment, therefore, in order to prevent the
magnetic core 2 from being saturated with the magnetic flux, the maximum amount is set for the magnetic flux which theexcitation coil 3 is made to generate, according to the temperature of themagnetic core 2. Referring toFIG. 6 , the maximum amount for the magnetic flux is set by converting the magnetic flux density into an equivalent amount of electric power, and then, the largest amount by which theexcitation coil 3 is supplied with electric power is set to the value of this equivalent amount of electric power. Setting the maximum amount by which theexcitation coil 3 is supplied with electric power is to control (limit) the maximum amount by which theexcitation coil 3 is allowed to be supplied with electric power. It is possible to obtain the relationship between the magnetic core temperature and the maximum amount by which theexcitation coil 3 is allowed to be supplied with electric power without causing themagnetic core 2 to be saturated with magnetic flux, fromFIGS. 5 and 6 . This relation is shown inFIG. 7 , in which a solid line represents the relationship between the core temperature and the maximum amount by which theexcitation coil 3 can be supplied with electric power without saturating theexcitation coil 3 with magnetic flux. In this embodiment, however, the maximum amount of electric power is set according to the magnetic core temperature as shown by a broken line inFIG. 7 . - In this embodiment, the largest amount by which the
excitation coil 3 is allowed to be supplied with electric power was set as shown in Table 1. Then, the length of time it took for the temperature of thefixation sleeve 1 to reach the level (target level) at which the fixing device A became ready for image fixation after electric power began to be supplied to theexcitation coil 3 when the magnetic core temperature was 25° C., 100° C., 150° C. and 180° C., was measured. - First example of comparative control: the maximum amount of electric power was set to 450 W regardless of the temperature of the
magnetic core 2. Also in the case of this setting, the length of time it took for thefixation sleeve 1 to reach the fixation-possible-temperature was measured. - Second example of comparative control: in order to prevent the
magnetic core 2 from being saturated with the magnetic flux, even if theexcitation coil 3 is supplied with 1500 W of electric power when the magnetic core temperature was 200° C., themagnetic core 2 was made to 250 mm2 in the size of its cross-section. Accordingly, thefixation sleeve 1 was increased in internal diameter to 40 mm. Also in the case of the comparative control, the length of time it took for the temperature of thefixation sleeve 1 to reach the fixation-possible-level was measured. - The results of the verification tests are shown in Table 2. In this embodiment, the target length of time for the temperature of the
fixation sleeve 1 to reach the fixation-possible-level was set to be no more than 7.5 seconds. -
TABLE 1 Core temp. 71- 121- 171- −70° C. 120° C. 1700° C. 200° C. Upper Embodiment 1500 W 1000 W 600 W 450 W limit of Comp. Ex. 450 W 450 W 450 W 450 W electric 1 power Comp. Ex. 1500 W 1500 W 1500 W 1500 W 2 -
TABLE 2 Core temp. 25° C. 100° C. 150° C. 180° C. Upper Embodiment 7.0 6.8 sec 7.0 sec 7.3 limit of sec sec electric Comp. Ex. 15.2 11.8 8.1 sec 7.3 power 1 sec sec sec Comp. Ex. 8.2 7.1 sec 6.1 sec 5.4 2 sec sec - In this embodiment, in a case where the magnetic core temperature is high, the maximum amount for the electric power is limited to small value. That is, the engine controlling section 43 (setting section) sets the maximum amount of electric power in such a manner that the higher the magnetic core temperature (obtained temperature) is, the smaller the maximum amount of electric power. However, because the fixing device itself may have warmed up, it does not require a large amount of heat to make the
fixation sleeve 1 reach the fixation-possible-temperature. Therefore, even if the maximum amount of electric power is small, it is possible to make thefixation sleeve 1 reach the fixation-possible-temperature in a short length of time. On the other hand, in a case where the magnetic core temperature is low, the maximum amount of electric power may be set to be larger. Therefore, even if the heating device itself has not warmed up, it is possible to make thefixation sleeve 1 reach the fixation-possible-temperature within a short length of time. - In comparison, in the case of the first example of comparative control, as long as the magnetic core temperature was high, it was possible to make the
fixation sleeve 1 reach the fixation-possible-temperature within a target length of time, as it was in the case of this embodiment. However, if the magnetic core temperature was low, it was impossible to make thefixation sleeve 1 reach the fixation-possible-temperature within the target length of time, because the amount by which theexcitation coil 3 was allowed to be supplied with electric power was limited to the same value as the value for a case in which the magnetic core temperature is high. - In the case of the second example of comparative control, the amount by which the
excitation coil 3 was supplied with electric power was kept at 1500 W regardless of the magnetic core temperature. However, because thefixation sleeve 1 was increased in internal diameter, it was greater in thermal capacity. Therefore, in a case where the magnetic core temperature was high, it was possible to make thefixation sleeve 1 reach the fixation-possible-temperature within the target length of time. On the other hand, in a case where the magnetic core temperature was low, it was impossible to make thefixation sleeve 1 reach the fixation-possible-temperature. - As described above, by providing the fixing device A with a means for detecting the temperature of its
magnetic core 2, and adjusting the maximum amount by which magnetic flux is allowed to be generated by theexcitation coil 3, according to the magnetic core temperature, it was possible to make thefixation sleeve 1 to reach the fixation-possible-temperature within a short length of time, even when themagnetic core 2 was reduced in size. - By the way, the method for limiting the maximum amount by which the
excitation coil 3 is supplied with electric power does not need to be limited to the one in this embodiment, which changes the amount in steps according to the magnetic core temperature. For example, such a method that changes the maximum amount in a step-less manner according to the magnetic core temperature may be employed. - Next, the second embodiment of the present invention is described. In the first embodiment, the temperature obtaining section for obtaining the temperature of the
magnetic core 2 was thetemperature detection element 14, with which themagnetic core 2 was provided. However, the temperature obtaining section for obtaining the temperature of themagnetic core 2 does not need to be limited to thetemperature detection element 14. For example, it may be such a means (temperature estimating means) that is for estimating (predicting) the magnetic core temperature. In the second embodiment, such a means was employed as the temperature obtaining section. - In the second embodiment, the magnetic core temperature is estimated based on the temperature detection history of the
temperature detection elements image forming apparatus 100. That is, the temperature obtaining section which obtains the temperature of themagnetic core 2 comprises: thetemperature detection elements fixation sleeve 1; and a temperature estimating section 43 (engine controlling section) which estimates the temperature of themagnetic core 2 based on the temperature detected by thesetemperature detection elements -
FIG. 8 shows the relationship among the measured temperature of thefixation sleeve 1, measured temperature of themagnetic core 2, and print count, when a substantial number of prints were continuously outputted. As the print count increased, the magnetic core temperature increased. More specifically, as the print count reached roughly 2,500, the magnetic core temperature reached 190° C. In particular, during the initial period of operation which was high in the rate of temperature increase, the magnetic core temperature increased roughly 90° C. while 500 prints were outputted. In other words, the rate of temperature increase was 0.18° C./print. Further, there seems to be virtually no correlation between the fixation sleeve temperature and magnetic core temperature. Next,FIG. 9 shows the relationship among the measure temperature of thefixation sleeve 1, measured temperature of themagnetic core 2, and elapsed length of time since the completion of the printing operation. As time elapsed since the completion of the printing operation, the magnetic core temperature gradually became closer to the fixation sleeve temperature. Further, after the elapse of roughly 3,000 seconds, it became the same as the fixation sleeve temperature. - Based on the results of the above described experiments, the
engine controlling section 43 estimates temperature T0, at which the magnetic core temperature will be at the starting of a printing operation, and temperature T1, at which the magnetic core temperature will be during the printing operation, as follows. -
T1=T0+0.18×n (however, if T1>190° C., T1 is assumed to be 190° C.) -
T0=T2−(T2−Ts)×t/3000. - n: print count
- T2: length of time having elapsed since the completion of the preceding job
- Ts: fixation sleeve temperature
- Table 3 shows the settings for the maximum amount of electric power. In this embodiment, the temperature of the magnetic core was estimated, unlike in the first embodiment. Therefore, the maximum amount of electric power was set to values which were slightly smaller than those in the first embodiment. Then, the length of time it took for the
fixation sleeve 1 to reach the fixation-possible-temperature after themagnetic core 2 began to be supplied with electric power was measured when the estimated temperature of themagnetic core 2 was 25° C., 100° C., 150° C. and 180° C. - For comparison, as the first example of comparative control, the maximum amount of electric power was set to 450 W regardless of the temperature of the
magnetic core 2. Then, the length of time it took for thefixation sleeve 1 to reach its fixation-possible-temperature was measured as it was in the tests in which the control in the first embodiment was verified. - Further, as the second example of comparative control, in order to prevent the
magnetic core 2 from becoming saturated with magnetic flux even if theexcitation coil 3 is supplied with 1,500 W of electric power when the magnetic core temperature is 200° C., themagnetic core 2 was made to be 250 mm2 in the size of its cross-section. Thus, thefixation sleeve 1 was increased in internal diameter to 40 mm. Then, the length of time it took for thefixation sleeve 1 to reach its fixation-possible-temperature was measured. - The results of the tests are shown in Table 3.
-
TABLE 3 Core temp. 71- 121- 171- −70° C. 120° C. 1700° C. 200° C. Upper Embodiment 1450 W 950 W 580 W 450 W limit of Comp. Ex. 450 W 450 W 450 W 450 W electric 1 power Comp. Ex. 1500 W 1500 W 1500 W 1500 W 2 -
TABLE 4 Core temp. 25° C. 100° C. 150° C. 180° C. Upper Embodiment 7.3 sec 7.1 sec 7.3 sec 7.3 sec limit of Comp. Ex. 15.2 11.8 8.1 sec 7.3 sec electric 1 sec sec power Comp. Ex. 8.2 sec 7.1 sec 6.1 sec 5.4 sec 2 - Also in the case of this embodiment, the length of time it took for the
fixation sleeve 1 to reach the fixation-possible-temperature was no more than 7.5 seconds, which is the target length of time. In comparison, in the case of the first and second examples of comparative control, when the magnetic core temperature was low, thefixation sleeve 1 did not reach the fixation-possible-temperature within the target length of time. - As described above, in this embodiment, the fixing device A was provided with a temperature estimating section for estimating the magnetic core temperature, and the maximum amount by which magnetic flux allowed to be generated by the
excitation coil 3 was changed according to the estimated temperature of themagnetic core 2. As a result, even when themagnetic core 2 was reduced in size, it was possible to make thefixation sleeve 1 reach its fixation-possible-temperature within a short length of time. - In this embodiment, the temperature of the
magnetic core 2 was estimated by mathematical calculation based on the temperature of thefixation sleeve 1 and the history of the preceding printing operation. However, it may be based on only the history of the preceding printing operation, or the temperature of thefixation sleeve 1, that the temperature of themagnetic core 2 is estimated. That is, the fixing device A was configured so that its temperature obtaining section was the temperature estimating section 43 (engine controlling section) which estimates the temperature of themagnetic core 2 based on the history of the printing operation carried out by theimage forming apparatus 100. - Further, in a case where the
image forming apparatus 100 is equipped with other temperature detection elements than those in the first embodiment (element which detects ambient temperature, element which detects internal temperature), the information obtained from the other temperature detection element can be used to more precisely estimate the temperature of themagnetic core 2. That is, the fixing device A is configured so that the temperature obtaining section is made up of a combination of a temperature detection element 15 (FIG. 4 ) which detects the ambient temperature of the internal space of theimage forming apparatus 100, and the temperature estimating section 43 (engine controlling section) which estimates the temperature of the magnetic core based on the temperature detected by thetemperature detection element 15. - Here, a fixing device includes not only a heating device for fixing an unfixed toner image on a sheet of recording medium to the sheet, but also, a heating device for applying heat and pressure to the temporarily or permanently fixed image on a sheet of recording medium for the second time to improve the image in glossiness.
- Moreover, in the first and second embodiments, the cylindrical and rotational heating member having the electrically
conductive layer 1 a was theflexible fixation sleeve 1. These embodiments, however, are not intended to limit the present invention is scope. For example, the cylindrical, flexible, and rotational heating member having the electricallyconductive layer 1 a may be a flexible endless belt which is suspended, and kept tensioned, by two or more belt suspending members, and which is rotationally (circularly) driven. Further, it may be a hard and hollow roller, for example, a piece of hollow pipe. - Further, in the first and second embodiments, the fixing device A was configured so that the electrically
conductive layer 1 a is made to generate heat (Joule's heat) by the electric current which flows through the electricallyconductive layer 1 a in the direction parallel to the circumferential direction of thelayer 1 a. However, the present invention is also applicable to a fixing device which is configured so that the electricallyconductive layer 1 a is made to generate heat (Joule's heat) by the eddy current induced in the electricallyconductive layer 1 a. - While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
- This application claims the benefit of Japanese Patent Application No. 2014-148611 filed on Jul. 22, 2014, which is hereby incorporated by reference herein in its entirety.
Claims (5)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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JP2014148611A JP2016024349A (en) | 2014-07-22 | 2014-07-22 | Fixing device and image forming apparatus |
JP2014-148611 | 2014-07-22 |
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US20160026123A1 true US20160026123A1 (en) | 2016-01-28 |
US9442440B2 US9442440B2 (en) | 2016-09-13 |
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US14/804,548 Active US9442440B2 (en) | 2014-07-22 | 2015-07-21 | Fixing device and image forming apparatus |
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Families Citing this family (5)
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US10452012B2 (en) | 2016-03-15 | 2019-10-22 | Canon Kabushiki Kaisha | Cylindrical fixing member, fixing device and image forming apparatus |
US11156949B2 (en) | 2017-01-19 | 2021-10-26 | Canon Kabushiki Kaisha | Image forming apparatus |
JP7350472B2 (en) | 2018-09-27 | 2023-09-26 | キヤノン株式会社 | image heating device |
JP7346108B2 (en) | 2019-07-05 | 2023-09-19 | キヤノン株式会社 | Fixing device and image forming device |
JP7375366B2 (en) * | 2019-08-22 | 2023-11-08 | 株式会社リコー | Fixing device and image forming device |
Family Cites Families (17)
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JPS51120451A (en) | 1975-04-15 | 1976-10-21 | Stanley Electric Co Ltd | Cylindrical heater |
JP4218478B2 (en) | 2003-09-22 | 2009-02-04 | 富士ゼロックス株式会社 | Electromagnetic induction heating device, fixing device, and control method of electromagnetic induction heating device |
JP2005099238A (en) | 2003-09-24 | 2005-04-14 | Konica Minolta Business Technologies Inc | Induction heat fixing apparatus and image forming device with the same mounted therein |
JP4537215B2 (en) | 2004-02-03 | 2010-09-01 | キヤノン株式会社 | Image heating device |
EP1569046A1 (en) | 2004-02-27 | 2005-08-31 | Canon Kabushiki Kaisha | Image-forming apparatus with a detector unit for detecting the temperature of a recording medium |
US7215899B2 (en) | 2004-02-27 | 2007-05-08 | Canon Kabushiki Kaisha | Image forming apparatus having temperature sensing element for sensing temperature of recording material |
JP2005316443A (en) | 2004-03-30 | 2005-11-10 | Canon Inc | Image-heating device and conveyance roller used for the device |
JP2006084821A (en) | 2004-09-16 | 2006-03-30 | Canon Inc | Heat fixing apparatus |
JP5031326B2 (en) | 2006-11-02 | 2012-09-19 | キヤノン株式会社 | Image forming apparatus provided with electromagnetic induction heating device |
JP5464902B2 (en) | 2008-05-30 | 2014-04-09 | キヤノン株式会社 | Fixing device |
JP2010102305A (en) | 2008-09-24 | 2010-05-06 | Canon Inc | Image forming apparatus |
JP5473433B2 (en) | 2009-06-30 | 2014-04-16 | キヤノン株式会社 | Image forming apparatus |
JP5839839B2 (en) | 2011-05-19 | 2016-01-06 | キヤノン株式会社 | Fixing device |
JP5871515B2 (en) | 2011-08-16 | 2016-03-01 | キヤノン株式会社 | Image forming apparatus and density information acquisition method |
JP6103913B2 (en) | 2012-12-11 | 2017-03-29 | キヤノン株式会社 | Fixing device |
JP6366265B2 (en) * | 2013-12-18 | 2018-08-01 | キヤノン株式会社 | Fixing device |
JP6366264B2 (en) * | 2013-12-18 | 2018-08-01 | キヤノン株式会社 | Image heating apparatus and image forming apparatus |
-
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US9442440B2 (en) | 2016-09-13 |
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